Eye Exams
Testing Visual Acuity :-The ability to distinguish between two close points is called as visual acuity. For example : It is 7.30 in the morning. You see a bus approaching. Is it your office bus? You cannot read the board stating its destination and have to ask a fellow traveler. He reads it out for you. So he has better visual acuity than you. That's how 'visual acuity ' affects your daily life! Does that mean, you have less than required visual ability? If you go to a doctor he will measure your visual ability. So lets discuss the methods to measure the visual acuities! Visual acuity is measured with visual acuity charts. Visual acuity charts -Distance Vision Chart -The person sits at 3 meters or at 10 feet, from the chart. If he can read just the top letter, his visual acuity is 6/60 or 20/200.If he can read, the second line, it is 6/36 or 20/100 and so on. The fraction 6/60 or 20/200 means, he can read from 6 meters, or 20 feet what a normal person can read from 60 meters or 200 feet. The best acuity is 6/6 or 20/20. An acuity of 6/5, is better than normal. You may have a refractive error and may need glasses. This is checked by refraction. If, not even the top letter is read, vision is taken as finger counting. If no finger counting is possible, the patient has to detect from which direction the light is being flashed. Near Vision Chart -This consists of a card, held at about 25 cm., from the eye. Proper lighting conditions should exist. The grading is done as N 1 to N 6 . Refraction is done and Visual acuity is retested with corrective glasses and recorded as vision with glasses correction. Pinhole vision -Vision is also sometimes tested with a dark glass with a tiny hole in center. Many cases of cataract and some other diseases, have better pinhole vision. |
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